In the field of semiconductor devices, how to distribute electric field intensity and how to avoid excessive local electric field intensity must be taken into account in design of semiconductor devices in order to increase breakdown voltages of devices and improve reliability of devices. Electric field distribution can be controlled by many ways, for example, modulating and doping active regions, adding field plates to reduce the maximum values of electric fields, and controlling shapes of electrodes to restrain electric field distribution.
For example, for a GaN-based high electron mobility transistor which is a kind of flat-channel field effect transistors, control of gate shape is one of the very important device manufacturing processes. A planar structure of a high electron mobility transistor will cause non-uniform distribution of electric field intensity. Especially when a high voltage exists between a source and a drain, a very high electric field intensity will occur at edges of a gate which are adjacent to the drain. FIG. 1 shows distribution of electric field intensity between a source and a drain during operation of a GaN-based high electron mobility transistor. It could be seen that there is a very high electric field intensity at edges of the gate which are adjacent to the drain, the device will be breakdown once the peak electric field exceeds a critical electric field of the GaN material. Since the withstand voltage of the device is integration of the electric field intensity between the gate and the drain, compared with an electric field having uniform distribution, the higher the electric field intensity at the edges of the gate is, the smaller the withstand voltage is. This phenomenon will greatly degrade device performances, such as breakdown voltages and reliability of devices.
For a Schottky diode, there is a local maximum value in an electric field at edges of the electrodes, there is a need to build a field plate or form a depletion layer at the edges in order to improve electric field distribution.
For a Laterally Diffused Metal Oxide Semiconductor (LDMOS) having a planar structure or a Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET) having a vertical structure, such as a U-shaped trench MOSFET (UMOSFET), there is a peak electric field at edges of electrodes, it is also necessary to control shapes of the electrodes or add field plates at the edges to improve electric field distribution. For a UMOS or a Vertically Diffused Metal Oxide Semiconductor (VDMOS) having a vertical structure, the electric field at the edges also needs to be controlled.
In order to change distribution of electric field intensity and improve operation performances of devices, electric field distribution can be controlled by many ways, for example, modulating and doping active regions, using field plates to reduce the maximum values of electric fields, and controlling the shapes of the electrodes to restrain electric field distribution.
Field plates are used to expand a horizontal depletion region of a planar device through vertical depletion for the active region of the planar device, causing change of distribution of electric field intensity of the planar device. The field plates can be disposed at a source, a gate or a drain. One or more than one field plate can be used in a device to change distribution of electric field intensity and reduce the maximum electric field intensity at edges of the gate which are adjacent to the drain. As a gate with a T shape, a T-gate is used to change distribution of electric field intensity with its own shape feature.
In processes of manufacturing field plates and T-gates, a dielectric layer is essential. The most common dielectric layers are made of silicon nitride. Due to limitation of manufacturing processes, it is difficult to implement a field plate having a complicated shape. That is, the processes may be very complicated, or there is no such a process which can achieve it. Similarly, due to limitation of manufacturing processes, the shapes of gates are always simple and it is difficult to manufacture gates having various shapes. That is, the processes may be very complicated, or there is no such a process which can achieve it. Thus it is required to develop new manufacturing processes to achieve field plates having complicated shapes and gates having various shapes.
Therefore, in order to address the above-mentioned technical problems, it is necessary to provide a semiconductor device and a manufacturing method therefor.